Portable mass data storage and data processing devices, such as portable disk drives, mobile phones, notebook computers, and personal data assistants (PDAs), must be provided with direct-current (DC) battery power for electrical charge or a built-in power supply for supplying DC power. However, the conventional DC power supply is primarily DC battery or cells. Each of the portable devices, such as the portable disk drives, the mobile phones, notebook computers, and personal data assistants, are not compatible thereamong in power supply so that a variety of DC batteries and corresponding chargers must be provided for different portable devices. This makes it difficult to carry and use these portable devices.
A compound battery charger is conventionally available for providing a variety of batteries with charging function. However, the conventional portable devices cannot perform the conversion and switch operations among different power supplies or input power sources based on the power management. Further, the conventional compound charging device uses a control chip to carry out the power management control. The control chip controls the management of the charging circuit and power sources by means of multiple sets of input/output (I/O) terminals. However, the number of the I/O terminals is proportional to the costs of design and manufacturing of the power management circuit. In other words, the charging device would be more costly if a control chip having more I/O terminals is used. This is adverse against industrial use and economic performance for manufacturing the charging device.
In addition, the conventional charging control device or compound charging device cannot automatically switch among different control functions to select the optimum charging and power supply operations based on the type of the input power source. This disadvantageously results in an excessive electrical current for charging operation and power supply operation. For example, in case the input power source is a USB-interfaced power source that supplies a small current, when charging to a lithium battery and power supply operation are both performed, power consumption will be significantly increased and the circuit will be over-loaded, which results in damage to the operation and parts of the circuit. Thus, this causes inconvenience and troubles in the applications of the conventional charging device and the conventional compound power supply. Consequently, there is a need to improve the conventional power management system to solve the aforementioned problems.